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RE: SCIENCE AND CLASSIFICATION
Dear All,
First of all, I would very strongly recommend that all systematists
read the 1998 paper by Eric B. Knox (Biological Journal of the Linnean
Society, 63:1-49; entitled "The use of hierarchies as organizational models
in systematics"). It's one of those rare "stand-out" papers that
occasionally punctuate the systematics literature every decade or so, but
not always fully appreciated in the years just after publication.
Anyway, I have been watching the bird-dinosaur debate for many, many
years, and have immersed myself more deeply into it for the past couple of
years. Even among the vast majority, who now agree that birds are dinosaur
descendants, there have already been endless debates over whether
mononykines are birds, or if Rahonavis is a bird, or Caudipteryx,
Protarchaeopteryx, Bambiraptor, Unenlagia ("half-bird"), Microraptor,
oviraptors, and so on (and then there's the Protoavis mess which is a story
unto itself).
My contention is that much of this confusion and needless wrangling is
no longer due to the lack of information, but rather due to the use of
Archaeopteryx as the basalmost bird (the cladistic definition I have
accepted, up to now, for the sake of stability in the short-term). But we
now have sufficient data to define Aves in a more scientifically rigorous
fashion (osteologically), just as was done with Mammalia decades ago. The
presence of hair and lactation roughly corresponds to the scientific
definition, so there have been no big problems reconciling the two
(communication went smoothly, at least until cladistic splintering muddled
it up with Mammaliamorpha and the like).
The new definition of Aves, if done correctly, will do for birds what
has so long been successfully done with mammals. The scientific definition
will be precise (osteological), but it will roughly coincide with the
presence of "vaned" feathers. All those more primitive "protofeathers" on
Sinosauropteryx, the newly-discovered pterosaur, and even that
bristly-tailed psittacosaur, are apparently just that (PROTOfeather
homologs). Whether the structures of Beipiaosaurus are best regarded as
advanced protofeathers or primitive vaned feathers remains to be seen. In
any case, a precise osteological definition should take precedence over
feathers, eggshells, origins of flight, and other characters that fossilize
poorly (and that obviously includes bird excrement as well). :-)
Within this new context, the evolution of brooding and powered flight,
the ornithoid eggshell evidence, and so on, will begin to make more sense,
and it will also clarify many of the debates that have paleontologists and
ornithologists insulting each other in the press and in other public forums
(fora?). The whole Longisquama debate is one of the more embarrassing
examples.
I am proposing a long-thought-out, moderate paradigm shift that I
believe will enhance stability. Both scientists and the public alike will
have to learn that the old "bird = feather possession" idea is inaccurate
and out-of-date. But shifting to the possession of "vaned" feathers seems
the best way to accomplish a smooth transition (especially with the public).
What we now have is confusion and taxonomic instability. The question in
my mind is not *whether* we should draw a new line, but *where* it should be
drawn. To continue drawing the line at Archaeopteryx (eclectically or
cladistically) is a tradition that I think we must abandon for everyone's
sake.
More generally, we are faced with a decision between: (1) an eclectic
emphasis on apomorphy (character)-based taxa or (2) a purely cladistic
emphasis on node- and stem-based taxa. The latter seems to sacrifice
stability of content in favor of stability of definition (definitions which
cladists are already fighting over, requiring a new bureaucratic code to
settle them, and no sign that its decisions will be widely followed anyway).
If you look at it from a broad perspective, all classifications are
arbitrary and "typological" to some degree, and pure cladism is just
promoting a new form of arbitrary "typology". Benton (2000) has already
pointed out that in the end, we will be no better off, and thatin many ways
we will be much worse off if we follow this path. The pendulum has swung
too far already (swinging so far, that even I have been ousted from the
"Cladists Club", which is very odd because some eclecticists think I'm too
much of a "cladist").
Anyway, I certainly look forward to Mickey Mortimer's upcoming
analysis. And I will seriously consider it's outcome as I continue
searching for a precise osteological definition of Aves that can be made
more precise in the future (as has been done with the Mammalia definition).
------ Cheers, Ken Kinman
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